The invention relates to a process for producing metal-sheathed strands, especially glass fiber cables, in which non-ductile or slightly ductile core material is placed in a profile consisting of a metal strip formed into a U-shaped cross-section which is then closed, so as to form a split tube carrying and/or protecting the core material. The split tube is subjected, after the welding of its longitudinal seam, to reductive processing.
Non-ductile and slightly ductile fibers, wires, and metal and non-metal tubes are sheathed in quasi-endless lengths by closed metal protective and carrying tubes to improve their use characteristics. Typical areas of application for the present invention are the sheathing of glass fibers used in telecommunications, particularly by steel sheaths, and the insertion of filaments in superconductors.
In a known process for producing metal-sheathed strands, a strip, e.g., a steel strip is formed into a U-shaped cross-section into which glass fibers suitable for data transmission are placed along with a gel as a lubricant and protective agent. The glass fibers are unwound from a coil and placed in practically continuous fashion into the strip, which is continuously unwound from a reel and formed into the U-shaped profile. After the glass fiber core material has been inserted, the U-shaped profile is shaped into a split tube. The remaining longitudinal seam is then closed by welding, and the formed tube is subjected to hollow drawing in a continuous drawing device.
A disadvantage of the known process is that it limits the possible reduction of the strand sheath to approximately 25%. A second drawing step in a downstream drawing machine is not possible, because, in the case of virtually endless cables, lengthening the drawn tube would tear the only slightly deformable fibers. In addition, hollow drawing results in thicker walls, so that the wall to be welded must be thinner than the finished wall. The relatively small welding sizes impair the productivity and profitability of the production process in the known unit. Furthermore, shaping the strip and inserting the core material are difficult in the case of relatively thin and narrow initial strips.
An object of the present invention is to provide a process and an apparatus for producing metal-sheathed strands which have the capability of greater stretching of the tube with the welded longitudinal seam, and which operate more economically with higher production rates and lower production costs.